Control circuit



1947- K. L. FREEMAN CONTROL CIRCUIT Filed Oct. 19, 1945 load /9 29 FM QCon/'ro/ INVENTOR K e/fhL/reeman.

ATTORN Va/faye WITNESSES: W

Patented Nov. 18, 1947 CONTROL CIRCUIT Keith L. Freeman, Swlsrvale, Pa.,aaaignor to Westinghouse Electric Corporation, East Pittsburgh, Pa.,acorporation of Pennsylvania Application October 19, 1945, Serial No;623,309

This invention relates to an electronic control system and hasparticular relation to a system for use in controlling the operation ofa load device, such as a relay, energized from an alternating voltagesource.

In many control or timing circuits, it is highly desirable to controlthe energization of a relay from alternating voltage supply lines by theoperation of an electric discharge valve of the arelike type, such as athyratron.

In addition, it is many times desirable to have the relay maintained inits energized position while the controlling thyratron is maintainednon-conductive, and changed to its deenergized position when thethyratron becomes conductive. Various circuit arrangements have beendevised in the past to accomplish the desired operations.

However, with the greatly increased application.

of electronic control circuits in industry, there has been acorresponding increase in the need for new, improved and simplifiedsystems requiring.

but a minimum number of parts in a' lesslcostly arrangement.

It is, accordingly, an object of my invention ,to provide a new and'improved'control system for controlling the operation of a load device,such as a relay, from an alternating voltage source.

It is another object of my invention to provide a new and improvedcontrol system for controlling the energization of a load device such asa relay from an alternating voltage source by means of an electricdischarge valve of the arclike type.

A further object of my invention is to provide a new and improvedcontrol system for controlling the energization of a relay from analternating voltage source by means of an electric discharge valve ofthe arc-like type in which the number of elements is maintained at aminimum in an inexpensive arrangement.

In accordance with my invention an alternating voltage systemis providedin which a relay may be maintained in its energized position while acontrol thyratron is non-conductive and in its deenergized position solong asthe control thyratron becomes conductive in each positivehaliperiod of the alternating voltage, that is, in each half-period inwhich the anode of the thyratron is positive with'respect to thecathode. The system employs a minimum number of elements and is simplein construction and operation.

The teatures of my invention. which I consider novel are set forth withmore particularity in the appended claims. The invention itself.however, together with additional objects and advantages thereof, may bebetter understood from the following description of a specificembodlment when read in connection with the acco'mpanying drawings. inwhich:

4 Claims. (Cl. 175-320) bodying my invention; and

Fix. 2 is a schematic diagram illustrating the structure of a thyratrontube employed in the circuit of Fig. 1.

As shown in Fig. 1. an electric discharge valve 3 of the arc-like type,such as a thyratron, has its anode I and cathode I connected in serieswith a current limiting resistor 8 and a control switch ll across a pairof alternating voltage supply lines It and It, A control circuit isprovided for the thyratron 3 and extends from the control grid l1thereof through a grid resistor it, a source of biasing voltageillustrated as a battery II, and a source of control voltage 23 to thecathode I.

The operating coil 25 of a direct current relay 21 is connectedin acircuit. extending from the anode 5 of the thyratron 3 to the shieldgrid 29 thereof. A capacitor is connected in shunt with the operatingcoil 25. The contact 3| of the relay 21 is arranged to complete acircuit through a load 33 when the relay 2'! is in its energizedposition.

The source of control voltage '23 may be any suitable source forestablishing a desired voltage between the control grid andcathode. Thecontrol grid to cathode voltage is to be variable or changeable in somemanner, as in accordance with some. electrical or physicalcondition, tocause the thyratron tobe maintained non-conductive at certain times whenit is desired to have the relay inits energized position and to causethe thyratron to become conductive in each positive half period of thealternating.v voltage when it is desired to have the relayvinits-deenersizell position. To do this, it is merely-necessary thatthe control voltage be such as tocausethe control grid to cathodevoltage to be-less positive than the critical control grid to cathodevoltage for the thyratron when the thyratron is to be maintainednon-conductive and more positive than the critical voltage when thethyratron is to be rendered conductive in positive half-periods.

To understand the operation of a circuit as shown in Fig. 1, thestructure of a typical thyratron having a shield grid, asshown in'Fig.2, must be considered. The usual thyratron having a shield grid, such,for example, asthe well known RCA 2050 thyratron or the WestinghouseWI,- 630A thyratron, includes a gas-filled envelope 35 having therein ananode 5 and a cathode I, the latter being heated by 'a filament 31. Acontrol grid I'Ijis also mounted within the envelope 35 becontrol gridarrangement I! with a partition 38 extending between the control grid l1and the-anode 5. This partition 39 is slotted atll to'perin'it the newofelectrons from the cathode I past the tion which is so positioned thatcurrent may flow 4 from the shield grid to the cathode while a controlgrid to cathode voltage exists which prevents current flow from theanode 5 to cathode I. It is ternatins voltage supply lines comprising an:;electric valve or the arc-liketype having an enivelope with .an anode'and a1 cathode therein evident, for example, that a portion of theshield grid structure is spaced from the cathode .1 on the opposite sidethereof from the control grid H so that current may flow from the'shieldgrid structure to the cathode 1 while the control grid to cathodevoltage is highly negative.

When a thyratron 3 having a structure as shown in Fig. 2, is employed inthe circuit of Fig. l, the operation of the circuit is as follows. Withthe switch i I closed and a control grid to cathode voltage establishedwhich prevents the thyratron from becoming conductive, current flowsfrom one of the supply lines i3 through the switch ii, the resistor 9,theoperating coil 25 of the relay 21, the shield grid 29 and cathode 1of the thyratron 3 to the other supply line during positive half-periodsof the alternating voltage. Current does not flow in this circuit duringthe negative half-period of the alternating voltage because of therectifier characteristics of the shield grid to cathode circuit withinthe thyratron 3. However, the capacitor 28 serves to maintain the relayenergized during the negative half-periods of the alternating voltage.In some cases, it may be desirable to use an alternating voltage relaywhich remains in an energized instead of a direct current relaywhereupon the capacitor may be omitted.

When the control grid to cathode voltage is changed by a change in thecontrol voltage so that the thyratron 3 becomes conductive in positivehalf-periods of the alternating voltage, the operating coil iseffectively short circuited during those positive half-periods havingonly the voltage drop between the anode and the shield grid thereacross.Consequently, the relay 2! is deenergized and the circuit through theload 33 is broken.

While I have shown and described a preferred embodiment of my invention,it is realized that many modifications thereof may be made withoutdeparting from the spirit of the invention. It is not my intention,therefore, to limit my invention to the specific embodiment illustrated.

I claim as my invention:

1. A control system for use with a pair of alternating voltage supplylines comprising an electrio valve of the arc-like type having anenvelope with an anode and a cathode therein adapted to be connected ina circuit across said lines, said envelope also having therein a controlgrid mounted between said cathode and anode and an auxiliary electrodespaced from said cathode with a portion positioned so that current mayflow from said auxiliary electrode portion to said cathode while a gridto cathode voltage exists preventing initiation of current flow fromsaid anode to cathode, a load device connected in a circuit extendingfrom said anode to said auxiliary electrode, and a control circuitextending from said grid to said cathode for establishing a. voltagebetween said grid and cathode causing said valve to be maintainednonconductive at certain times and to be rendered conductive in positivehalf-periods of said alternating voltage at other times. 7

2. A control system for use with a pair of a1- adapted to be connectedin a circuit across said lines. said envelope also having therein acontrol grid mounted between said cathode and anode and an auxiliaryelectrode spaced from said cathode with a portion positioned so thatcurrent may flow from said auxiliary electrode to said cathode while agrid to cathode voltage exists preventing initiation or current flowfrom said anode to cathode, a relay having an operating coil, connectedin a circuit extending irom said anode to said auxiliary electrode, anda control circuit extending from said grid to said cathode forestablishing a voltage between said grid and cathode causing said valveto be maintained non-conductive at certain times and to be renderedconductive in positive halt-periods of said alternating voltage at othertimes, said relay being operable in response to substantial currentthrough said operating coil in each positive haliperiod of each periodof said alternating voltage.

3. A control system for use with a pair of alternating voltage supplylines comprising an electric valve of the arc-like type having anenvelope with an anode and a cathode therein adapted to be connected ina circuit across said lines. said envelope also having therein a controlgrid mounted between said cathode and anode and an auxiliary gridmounted between said control grid and anode but with a portion extendingon the opposite side oi said cathode from said control grid wherebycurrent may flow from said auxiliary grid to said cathode while acontrol grid to cathode voltage exists preventing initiation or currentflow from said anode to said cathode, a load device connected in acircuit extending from said anode to said auxiliary grid. and a controlcircuit extending from said control rid to said cathode for establishinga voltage therebetween causing said valve to be maintainednon-conductive at certain times and to be rendered conductive inpositive half-periods of said alternating voltage at other times.

4. A control system for use with a pair of alternating voltage supplylines comprising an electric valve of the arc-like type having anenvelope with an anode and a cathode therein adapted to be connected ina circuit across said lines, said envelope also having therein a controlgrid mounted between said cathode and anode and an auxiliary gridmounted between said control grid and anode with a portion extending onthe opposite side of said cathode from said control grid whereby currentmay flow from said auxiliary grid to said cathode while a control gridto cathode voltage exists preventing initiation 01' current flow fromsaid anode to said cathode, a relay having an operating coil connectedina circuit extending from said anode to said auxiliary grid, and acontrol circuit extending from said control grid to said cathode forestablishing a voltage therebetween causing said valveto be maintainednon-conductive at certain times and to be rendered conductive inpositive half-periods of said alternating voltage at other times,whereby a substantialcurrent flows through said operating coil only inpositive half-periods or said alternating voltage in which said valve isnon-conductive, said relay being operable in response to suchsubstantial current through said operating coil.

KEITH L. FREEMAN.

